Flight crew descends 400 ft below assigned altitude and turns off route to avoid C-5.

Attributes
ACN	317434
Time
Date	199509
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : dpk
State Reference	NY
Altitude	msl bound lower : 19600 msl bound upper : 20000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zbw
Operator	common carrier : air carrier
Make Model Name	B737-200
Operating Under FAR Part	Part 121
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : instrument pilot : commercial pilot : atp
Experience	flight time last 90 days : 143 flight time total : 16000 flight time type : 340
ASRS Report	317434
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	altitude deviation : overshoot non adherence : clearance non adherence : required legal separation other spatial deviation
Independent Detector	other controllera
Resolutory Action	flight crew : regained aircraft control flight crew : returned to intended course or assigned course other
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Having received a descent clearance from ZBW from FL220 to FL200, I reset the altitude reminder and received acknowledgement from my copilot. My copilot started the autoplt engaged descent from FL220. At this time I told my copilot that I would be off ATC frequency to get ATIS at swf and also to call company with arrival message. My copilot acknowledged. I then looked down into my flight bag to my left for the frequency information, shortly thereafter, I heard altitude warning go off. I looked up, immediately went back to ATC frequency and controller said 'verify your altitude at FL200.' seeing FL196 on my altimeter, I said 'get on your altitude' and then told ATC that we were 'leveling at FL200.' my copilot told me that she had a TA warning and that she had been visually watching a C-5A ahead and to the right. Apparently not comfortable with his altitude and/or our rate of closure, she had made a slight left turn and took an evasive posture in relation to the C-5A, including the altitude deviation. At this point, the TA was over and we were well clear of the traffic. I personally did not see or hear the TA. In that my head was down to the left and, in that the traffic ahead was to the right, I could not evaluate my copilot's evasive action but she said that she did what she had done evasively for what she thought was for good reason. Shortly thereafter, I told the controller that we had a traffic alert and he then gave me ZBW telephone number for quality assurance. I was told to call during normal business hours during the week. I complied by speaking with ATC representative on oct/xx/95. I do believe that because of the massive size of the C-5A, it would appear larger and thus closer than it really was. Since visibility was so good and because my copilot was intently, visually fixed on the traffic in order to assure being well-clear, the altitude deviation occurred. With safety in mind, I believe my copilot used the 'see and avoid' principle and considered that paramount in flying the airplane in order to be sure of avoiding any possible conflict.

Original NASA ASRS Text

Title: FLC DSNDS 400 FT BELOW ASSIGNED ALT AND TURNS OFF RTE TO AVOID C-5.

Narrative: HAVING RECEIVED A DSCNT CLRNC FROM ZBW FROM FL220 TO FL200, I RESET THE ALT REMINDER AND RECEIVED ACKNOWLEDGEMENT FROM MY COPLT. MY COPLT STARTED THE AUTOPLT ENGAGED DSCNT FROM FL220. AT THIS TIME I TOLD MY COPLT THAT I WOULD BE OFF ATC FREQ TO GET ATIS AT SWF AND ALSO TO CALL COMPANY WITH ARR MESSAGE. MY COPLT ACKNOWLEDGED. I THEN LOOKED DOWN INTO MY FLT BAG TO MY L FOR THE FREQ INFO, SHORTLY THEREAFTER, I HEARD ALT WARNING GO OFF. I LOOKED UP, IMMEDIATELY WENT BACK TO ATC FREQ AND CTLR SAID 'VERIFY YOUR ALT AT FL200.' SEEING FL196 ON MY ALTIMETER, I SAID 'GET ON YOUR ALT' AND THEN TOLD ATC THAT WE WERE 'LEVELING AT FL200.' MY COPLT TOLD ME THAT SHE HAD A TA WARNING AND THAT SHE HAD BEEN VISUALLY WATCHING A C-5A AHEAD AND TO THE R. APPARENTLY NOT COMFORTABLE WITH HIS ALT AND/OR OUR RATE OF CLOSURE, SHE HAD MADE A SLIGHT L TURN AND TOOK AN EVASIVE POSTURE IN RELATION TO THE C-5A, INCLUDING THE ALTDEV. AT THIS POINT, THE TA WAS OVER AND WE WERE WELL CLR OF THE TFC. I PERSONALLY DID NOT SEE OR HEAR THE TA. IN THAT MY HEAD WAS DOWN TO THE L AND, IN THAT THE TFC AHEAD WAS TO THE R, I COULD NOT EVALUATE MY COPLT'S EVASIVE ACTION BUT SHE SAID THAT SHE DID WHAT SHE HAD DONE EVASIVELY FOR WHAT SHE THOUGHT WAS FOR GOOD REASON. SHORTLY THEREAFTER, I TOLD THE CTLR THAT WE HAD A TFC ALERT AND HE THEN GAVE ME ZBW TELEPHONE NUMBER FOR QUALITY ASSURANCE. I WAS TOLD TO CALL DURING NORMAL BUSINESS HRS DURING THE WEEK. I COMPLIED BY SPEAKING WITH ATC REPRESENTATIVE ON OCT/XX/95. I DO BELIEVE THAT BECAUSE OF THE MASSIVE SIZE OF THE C-5A, IT WOULD APPEAR LARGER AND THUS CLOSER THAN IT REALLY WAS. SINCE VISIBILITY WAS SO GOOD AND BECAUSE MY COPLT WAS INTENTLY, VISUALLY FIXED ON THE TFC IN ORDER TO ASSURE BEING WELL-CLR, THE ALTDEV OCCURRED. WITH SAFETY IN MIND, I BELIEVE MY COPLT USED THE 'SEE AND AVOID' PRINCIPLE AND CONSIDERED THAT PARAMOUNT IN FLYING THE AIRPLANE IN ORDER TO BE SURE OF AVOIDING ANY POSSIBLE CONFLICT.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.